This invention relates to a wire grid polarizer and also to a liquid crystal display device of transmission type which uses such a wire grid polarizer and a liquid crystal display device of transflective type which uses such a wire grid polarizer and enjoys both transmission and reflection types of display.
U.S. Pat. No. 6,348,995 discloses a reflection type image display device which provides image display by using polarized light reflected from the wire grid polarizer formed of thin closely spaced conductive elements disposed on the wavy surface of the substrate in the image display device, in order to reduce parallax and specular reflection and to improve contrast. The polarized light that passes through the wire grid polarizer is absorbed in the light absorbing layer dispose on the rear surface of the wire grid polarizer.
JP-A-2005-250430 discloses a liquid crystal display (hereafter referred to also as LCD) device, intended for improved image quality and reduction in size, comprising the first plate whose pixel portion is provided with light reflection and transmission sections, the second plate disposed at a distance opposite to the first plate, and the liquid crystal layer interposed between the first and the second plates, wherein the polarizing layer is formed at least on that part of the surface of the first plate which is adjacent to the liquid crystal layer and corresponds to the light reflecting section.
SID (Society of Information Display) 06 Digest, 2006, p. 89, discloses a 3-D display using a transmission type liquid crystal display incorporating therein a wire grid polarizer.
The wire grid polarizer used in the liquid crystal display device disclosed in U.S. Pat. No. 6,348,995 belongs to the reflective type light polarizer, and therefore is different from the polarizer of light absorption type. This reflective type polarizer is transparent to light of one polarization orientation while it reflects light of another polarization orientation perpendicular to the one polarization. Accordingly, the contrast of the reflection type LCD device can be improved by incorporating the wire grid polarizer in the LCD device itself. However, if the disclosed configuration is used in the LCD device having a light transmission section, a problem arises that contrast is lowered in a brightly illuminated ambience due to the polarized light reflected from the wire grid polarizer.
If a wire grid polarizer is used in a transmission type LCD device as proposed in the SID 06 Digest, an image of good quality can be observed as a result of the transmission of backlight in a dim ambience. However, there will arise a problem that in the brightly illuminated ambience the image quality is degraded due to the degradation of contrast caused by the reflection of ambience light.
Also, JP-A-2005-250430 discloses a coating type polarizing material to serve as a polarizing layer disposed on that surface of the first plate which faces the liquid crystal layer. However, such a coating type polarizer has a problem that it is inferior in performance to an ordinary polarizer which is attached externally to an LCD device. Accordingly, in order to improve contrast, the coating type polarizer should not be used singly, but must be accompanied by an external polarizer.
Further, U.S. Pat. No. 6,348,995 suggests that the polarization performance of such a coating type polarizing layer is insufficient and suggest that an additional polarizer should be provided on the surface of the first plate opposite to the liquid crystal layer to obtain high contrast and therefore improved image quality.